Prior Electron Beam Memory Systems
The technological society in which we live appears to have an insatiable appetite for the storage of data, but there is a significant mismatch between the amount of data (particularly in digital form) and the devices currently available to store such data.
Examples of the need for digital storage are not difficult to find. Computer programs of 10-100 megabytes are not uncommon. To simply record social data in our population of 250 million people might require 10.sup.6 megabytes of storage. Images of various forms need considerable storage capacity--a single television frame may require two megabytes while a full color page of a magazine needs 10 times that amount. A year's supply of images from a single LANDSTAT satellite system has been estimated at 10.sup.15 bits.
It is also very apparent that the new Fifth Generation Computer will require a vast data base for its effective implementation. One might consider a base as large as the Library of Congress with perhaps 10.sup.16 bits.
Presently available data storage devices are totally inadequate to store this volume of digital information. For example, a magnetic hard disc system can typically store about 4.times.10.sup.9 bits of information. Optical disc systems can store in the order of 5.times.10.sup.10 bits. There is an obvious need, then, for a system which could store 10.sup.14 bits or more of information in digital form.
There are also substantial benefits which are not quite so apparent. For example, the existence of a vast memory on line would obviate destroying interim data and would allow its retrieval at any time. In such areas as image processing for a program development, this could be a very substantial benefit.
It is perhaps obvious that in order to develop memories of substantially greater storage capacity, resort must be had to the use of electrons or other charged particles with wavelengths less than the wavelength of light, or a system which does not depend upon radiation. Visible light is entirely inadequate; optical storage systems are already close to the wavelength limit of visible light.
Electron beam recording and retrieval of information has been explored for many years in laboratories and in some cases, practiced commercially. In the television field, there has been developed the now-commercial diffraction-type optical projection system in which electrostatic charges are deposited by an electron beam on a thermally softenable tape. Upon heating of the tape, the surface of the tape is deformed in accordance with the pattern of electrostatic charges. The television picture information stored on the surface-deformed tape is displayed by projecting a coherent beam of light through the transparent tape and spatially filtering the information diffracted by the surface deformations (R1, R2). An exhaustive treatment of television recording is given by Abramson (R2A).
Another approach is disclosed in the literature which follows this same general electron recording beam technique, but electron beams are used to read out the stored information by detection of emitted secondary electrons (R3). The literature describes a similar disc-based system which can be played mechanically, as well as by the use of electron beams to stimulate secondary emission from the thermoplastic medium (R4, R5, R6). There is also disclosed the application of the same thermoplastic recording technique in a real-time disc, tape or drum mass memory electron beam reading/erasing system with simultaneous optical read-out in vacuum (R7).
Others have suggested using electron beam recording to make mechanically readable video disc grooves by using a laterally vibrated electron beam to form the grooves in the disc (R6, R8).
Electron beams have been used to read out the surface deformations formed on an electrostatically deformed thermoplastic medium which has been negatively charged to create an electron mirror at the medium surface (R9).
Substantial engineering efforts have been expended developing video disc recording and retrieval technology--mainly optical and mechanical, but also using electron beams. An electron beam recording system has been developed for making the masters for capacitance-based (mechanical) video disc systems (R10). The prior art also includes a technique for an archival electron beam accessed memory in which a high intensity electron beam selectively melts columnar bits in a two-dimensional lattice supported by a thin membrane (R11).
It is clear that a disc-based system is best for quick access to high density information. In spite of the obvious need for an ultra-high density memory system and the obvious choice of electron beam radiation as the means by which the information is stored, no practical electron beam memory system has yet been developed because of the inability of the art to develop an electron gun having the requisite properties and capabilities.